Abgar the Great was most remembered for his alleged conversion to Christianity in about 200 CE and the declaration of Christianity as the official religion of the city at that time.[5][12][13]
It has been suggested that a cross shown on the tiara of Abgar VIII in coins he minted have Christian meaning.[14]

Osrhoene was a client state of the Roman Empire in this era,[1] Prior to Abgar VIII, in 165 CE, the Roman military had reinstated Abgar VII,[15] and they continued to have a significant presence in the region. However, Abgar VIII's behavior indicates that he was not wholly loyal to Rome nor was closely monitored by Rome. While Abgar VIII's coins bear the image of the Roman Emperor Commodus, Abgar's goals were to maintain a degree of independence and to extend his influence geographically as much as possible without disturbing the greater powers of Rome and Parthia.[7]
Abgar VIII supported Pescennius Niger as Roman Emperor in 193 CE, who was swiftly challenged and deposed by the Emperor Septimius Severus. Abgar VIII's submission to Septimus Severus is portrayed on the Arch of Severus in Rome. He was not deposed, but Osrhoene was made a Roman province and Abgar's kingdom was reduced to a rump state containing just the city of Edessa.[2] Abgar was fully reconciled with Septimus Severus and was later received with honor as a guest of Septimus Severus in Rome. In an additional display of loyalty, Abgar VIII took Severus' name as his own.[1]

Christianity spread in Edessa significantly during Abgar VIII's reign.[1] The Chronicle of Edessa (540 CE) reports that a Christian church building in Edessa was damaged in a flood in November 201 CE.[1] The Christian philosopher Bardaisan lived in Abgar VIII's court.[3]

Upon his death in 212 CE,[6] Abgar the Great was succeeded by his son Abgar IX surnamed Severus in contemporary Roman fashion. Though Abgar Severus was summoned with his son to Rome in 213 CE and murdered at the orders of Caracalla.[16] A year later Caracalla ended the independence of Osroene and incorporated it as a province into Roman Empire.[17]